LAUSR

Abstract Weirs play a decisive role in the safety of dams. There are different types of weirs including labyrinth, linear, arced, piano key, etc. Arced weir is an arc of a circle which makes possible an increase in the effective length of the weir crest at a specific width, and thus enabling a greater discharge to pass through the weir for a specific hydraulic load. This study attempted to investigate the Discharge Coefficient and the discharge which passes through direct and arced weirs in linear and triangular labyrinth modes in the laboratory. The Discharge Coefficient of these weirs, which is a function of the ratio of the total hydraulic load to the weir crest height ( H d / P ), is compared given the effect of the weir shape and their hydraulic performance. The results show that the increased ( H d / P ) value leads to a decreased Discharge Coefficient in all weirs. The amount of the aforesaid decrease varies depending on weir type reaching up to 20% and 51% in the linear weir and the labyrinth weir respectively. Moreover, the increased effective length of the weir as a result of its arced shape resulted in improved efficiency of linear arced weirs and labyrinth arced weirs up to 21% and 57% respectively. With hydraulic load increasing, the height of standing wave at the downstream of arced weirs increased leading to a decreased efficiency of arced weirs.